U.S. patent number 4,850,962 [Application Number 07/165,594] was granted by the patent office on 1989-07-25 for implantable hearing aid and method of improving hearing.
This patent grant is currently assigned to Medical Devices Group, Inc.. Invention is credited to Donald W. Schaefer.
United States Patent |
4,850,962 |
Schaefer |
July 25, 1989 |
Implantable hearing aid and method of improving hearing
Abstract
A method and apparatus are disclosed for improving the hearing
of a hearing-impaired subject who, if anatomically normal,
possesses a tympanic membrane intended for generating mechanical
tympanic vibrations in response to sound waves impinging thereon,
an inner ear responsive to mechanical vibrations, and an ossicular
chain intended to communicate mechanical vibrations from the
tympanic membrane to the inner ear; wherein the ossicular chain is
interrupted to preclude transmission of mechanical vibrations
between the tympanic membrane and the inner ear of the subject and
an implant is surgically interposed within the ossicular chain to
form an independent link between the tympanic membrane and the
inner ear, which implant is comprised of a transducer for
converting mechanical signals generated at the tympanic membrane
into electrical signals for direct electrical stimulation of the
inner ear.
Inventors: |
Schaefer; Donald W.
(Belleville, WI) |
Assignee: |
Medical Devices Group, Inc.
(Madison, WI)
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Family
ID: |
27389169 |
Appl.
No.: |
07/165,594 |
Filed: |
March 8, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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895156 |
Aug 11, 1986 |
4729366 |
Mar 8, 1988 |
|
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677638 |
Dec 4, 1984 |
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Current U.S.
Class: |
600/25;
607/57 |
Current CPC
Class: |
A61N
1/36038 (20170801); A61F 11/04 (20130101); A61F
2/18 (20130101); H04R 25/606 (20130101); A61F
2002/183 (20130101) |
Current International
Class: |
A61F
11/04 (20060101); A61F 11/00 (20060101); A61F
2/18 (20060101); A61N 1/36 (20060101); H04R
25/00 (20060101); H04R 025/00 () |
Field of
Search: |
;128/419R,421,784,789,1R,420.5,420.6 ;381/68.3 ;600/25 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Jako, "Biomed Eng. in Ear Surgery", Otolaryngolic Clinics of N.
America, vol. #5, Feb./72. .
T. Ono--Implantable Hearing Aid (Pt 1), Audecibal, Fall '84. .
Audiological Assessment of Vibratory Hearing, 17th Int. Congress of
Audiology, Aug. '84, Santa Barbara, Calif. .
Sako et al., "Conservative Tympanoplasty", Amer. Academy of
Opthalmology & Otolarynology, Course 319, Oct. 1, 1966. .
Article from The American Journal of Otology/vol. 5, No. 4, 4/84
entitled "Sound Pickup Utilizing an Implatable Piezoelectric
Ceramic Bimorph Element--Application to the Cochlear Implant".
.
Article from "Hearing Instruments" vol. 32, No. 9, 1981/13 entitled
"The Cochlear Implant: Performance of Deaf Patients"/Dr. House et
al. .
Copy of "Hearing Instruments" Jun. 1985 devoted to The Cochlear
Implant--1985; Copies of all excerpts included..
|
Primary Examiner: Hindenburg; Max
Assistant Examiner: Lacyk; J. P.
Attorney, Agent or Firm: Foley & Lardner
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of application Ser. No.
895,156 filed Aug. 11, 1986, for which a U.S. Pat. No. of 4,729,366
and an issue date of Mar. 8, 1988 have been assigned, which is in
turn a continuation-in-part of application Ser. No. 77,638 filed
Dec. 4, 1984, now abandoned.
Claims
What is claimed:
1. A method for improving the hearing of a hearing-impaired
subject, said subject, if anatomically normal, having a tympanic
membrane for generating mechanical tympanic vibration in response
to sound waves impinging thereon, an inner ear capable of
phonoreception, and an ossicular chain comprising an incus, a
malleus, and a stapes, intended for communicating mechanical
vibrations from said tympanic membrane to said inner ear, said
method comprising the steps of:
interrupting said ossicular chain to preclude transmission of said
mechanical vibrations between said tympanic membrane and said inner
ear of said subject; and,
surgically interposing an implant within said ossicular chain,
between said tympanic membrane and said inner ear to facilitate
electrical stimulation of the auditory nerve, said implant
comprising:
transducer means for converting said mechanical vibrations to
electrical signals, having controlled amplification
characteristics; and
transmission means for communicating said electrical signals from
said transducer means to said inner ear;
wherein said transducer means includes means operatively associated
with said tympanic membrane for receiving mechanical tympanic
vibrations therefrom and converting the same into electrical
signals characteristic thereof.
2. The method of claim 1, wherein said interrupting step comprises
removing at least one of the component parts from said ossicular
chain.
3. The method of claim 2, wherein said interrupting step comprises
removing the incus from the ossicular chain.
4. The method of claim 1, wherein said step of surgically
interposing said implant comprises disposing a mechanical to
electrical transducer, for generating electrical signals
characteristic of said mechanical vibrations of said tympanic
membrane, within the middle ear space of said subject; and
effecting a mechanical connection between an element of the
ossicular chain and said transducer.
5. The method of claim 4, wherein said step of effecting a
mechanical connection comprises mounting said transducer on the
malleus.
6. The method of claim 4, wherein said step of effecting a
mechanical connection comprises mounting said transducer on the
head of said malleus.
7. The method of claim 4, wherein said transducer comprises a
piezoelectric accelerometer.
8. The method of claim 1, wherein said implant further comprises a
power source.
9. The method of claim 1, further comprising the step of disposing
a power source, for supplying power to said implant, external to
said subject.
10. The method of claim 1, wherein said transmission means
comprises a proximal end in operative electrical communication with
said transducer means and a distal end in electrical communication
with said inner ear for transmitting electric signals from said
transducer to said inner ear.
11. The method of claim 10, wherein said step of surgically
interposing said implant comprises disposing said distal end of
said transmission means within the cochlea of said subject
proximate the auditory nerve fibers thereof for electrical
stimulation of said nerve fibers to represent sound energy
impinging on said tympanic membrane.
12. The method of claim 11, wherein said step of disposing said
distal end of said transmission means in said cochlea comprises the
steps of removing the stapes and penetrating the oval window to
facilitate invasion of the interior of said inner ear by said
transmission means.
13. The method of claim 11, wherein said step of disposing said
distal end of said transmission means comprises the steps of:
drilling a hole in the footplate of said stapes;
guiding said distal end of said transmission means through said
hole; and
penetrating the oval window to effect invasion of the interior of
said inner ear by said transmission means.
14. The method of claim 11, wherein the step of disposing said
distal end of said transmission means comprises penetrating the
round window to effect invasion of the interior of said inner ear
by said transmission means.
15. The method of claim 10, wherein said step of disposing said
transmission means in said cochlea comprises the step of securing
said distal end of said transmission means to the promontory to
establish electrical communication between said transducer means
and said inner ear.
16. An implantable apparatus for improving the hearing of a
hearing-impaired subject, said subject, if anatomically normal,
having a tympanic membrane for generating mechanical tympanic
vibrations in response to sound waves impinging thereon, and an
ossicular chain comprising an incus, a malleus, and a stapes for
communicating said tympanic vibrations to the inner ear of said
subject, said apparatus comprising:
transducer means for converting said tympanic vibrations to
electrical signals, having controlled amplification
characteristics, configured for bridging disposition in an
interrupted ossicular chain of said subject as an independent
electromechanical link between said tympanic membrane and said
inner ear of said subject, said transducer means disposed in
operative association with said tympanic membrane for receiving
mechanical tympanic vibrations therefrom and converting the same
into electrical signals characteristic thereof; and
transmission means for communicating said electrical signals from
said transducer means to said inner ear for effecting electrical
stimulation thereof.
17. The apparatus of claim 16, further comprising a power supply
electromagnetically associated therewith.
18. The apparatus of claim 17, wherein said power supply is
disposed externally of said subject.
19. The apparatus of claim 16, wherein said transmission means
comprises:
an electrical conduit having a proximal end in operative electrical
communication with said transducer means and a distal end in
operative electrical communication with said inner ear.
20. The apparatus of claim 16, wherein said transducer means is
disposed proximate said malleus for operative association
therewith.
21. The apparatus of claim 20, wherein said transducer means is
mounted on the head of said malleus.
22. The apparatus of claim 20, wherein said transducer means is a
piezoelectric accelerometer.
23. The apparatus of claim 19, wherein said transmission means is
an electrically conductive wire.
24. The apparatus of claim 19, wherein said distal end of said
transmission means is configured for electrical contact with the
promontory.
25. The apparatus of claim 19, wherein said distal end of said
transmission means is disposed interiorly of said inner ear.
26. The apparatus of claim 25, wherein said distal end of said
transmission means extends through the stapes, through the oval
window, and into said inner ear.
27. The apparatus of claim 25, wherein said distal end of said
transmission means extends through the round window and into said
inner ear.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a device for improving the
impaired hearing of a human subject, and more particularly, to an
implantable hearing aid device.
In an anatomically normal human hearing apparatus, sound waves,
which represent acoustical energy, are directed into an ear canal
by the outer ear (pinna) and impinge upon a tympanic membrane
(eardrum) interposed, at the terminus of the ear canal, between it
and the middle ear space. The pressure of the sound waves effect
tympanic vibrations in the eardrum, which then become manifested as
mechanical energy. The mechanical energy in the form of tympanic
vibrations is communicated to the inner ear by a sequence of
articulating bones located in the middle ear space, which are
generally referred to as the ossicular chain. The ossicular chain
must be intact if acoustical energy existing at the eardrum is to
be conducted as mechanical energy to the inner ear.
The ossicular chain includes three primary components, the malleus,
the incus and the stapes. The malleus includes respective
manubrium, neck and head portions. The manubrium of the malleus
attaches to the tympanic membrane at a point known as the umbo. The
head of the melleus, connected to the manubrium by the neck
portion, articulates with one end of the incus, which provides a
transmission path for the mechanical energy of induced vibrations
from the malleus to the stapes. The stapes includes a capitulum
portion connected to a footplate portion by means of a support crus
and is disposed in and against a membrane-covered opening to the
inner ear referred to as the oval window. The incus articulates the
capitulum of the stapes to complete the mechanical transmission
path.
Normally, tympanic vibrations are mechanically conducted through
the malleus, incus and stapes, to the oval window and therethrough
to the inner ear (cochlea). These mechanical vibrations generate
fluidic motion (transmitted as hydraulic energy) within the
cochlea. Pressures generated in the cochlea by fluidic motion are
accommodated by a second membrane-covered opening between the inner
and middle ear, referred to as the round window. The cochlea
translates the fluidic motion into neural impulses corresponding to
sound perception as interpreted by the brain. However, various
disorders of the tympanic membrane, ossicular chain and/or inner
ear can occur to disrupt or impair normal hearing.
Various passive mechanical ossicular prosthesis and implantation
techniques have been developed in connection with reconstructive
surgery of the middle ear. See G. J. Jako, "Biomedical Engineering
in Ear Surgery", Otolaryngoloqic Clinics of North America, Vol. 5,
No. 1, Feb. 1972, and G. J. Jako, et al., "Conservative
Tympanoplasty", American Academy of Opthalmology and Otolarynology,
Course 319, presented Oct. 1, 1966.
Miniaturized electronic hearing aid devices which compensate for
hearing disorders are also, in general, well known. Various of such
devices are adapted to be entirely received within the ear canal or
partly or completely implanted within the skull of a subject.
Examples of such devices are those disclosed in U.S. Pat. Nos.
3,170,046, issued to L. P. Leale on Feb. 16, 1965; 3,712,962 issued
to J. M. Epley on Jan. 23, 1973; 3,764,748 issued to J. P. Branch
et al. on Oct. 9, 1973; 3,346,704 and 3,557,775 issued on Oct. 10,
1967 and Jan. 26, 1971, respectively to J. L. Mahoney; 3,870,832
issued to J. M. Fredrickson on Mar. 11, 1975; 4,150,262 issued to
H. Ono on Apr. 17, 1979; 4,284,856 and 4,357,497 both issued to I.
J. Hochmaier et al. on Aug. 18, 1981 and Nov. 2, 1982,
respectively. Further description of such devices is found in T.
Ohno, "The Implantable Hearing Aid" (Part I) Audecibel, Fall 1984
and Aritomo et al., "Audiological Assessment of Vibratory Hearing"
presented at 17th International Congress of Audiology meeting,
Santa Barbara, Calif., Aug. 1984. See also, K. Gyo, N. Yanagihara,
and H. Araki, "Sound Pickup Utilizing an Implantable Piezoelectric
Ceramic Bimorph Element: Application to the Cochlear Implant",
American Journal of Ontology, Vol. 5, No. 4, April 1984.
Perhaps the most interesting of the aforementioned United States
patents is the '748 patent which concerns implantable hearing aids
including those which are configured for disposition principally
within the middle ear space. The approach suggested there provides
a transducer, which may be a piezoelectric crystal transducer,
capable of converting mechanical vibration, within the ossicular
chain into an output voltage. That output voltage may be applied to
the area of the oval window to electrically stimulate it and may
include a diode to rectify the variable voltage output of the
transducer into a pulsating DC voltage to stimulate the auditory
nerve. In another variant, the patentees suggest the incorporation
of a piezoelectric crystal in the area of the oval window which
receives the variable voltage signals from the transducer and
vibrates to stimulate the auditory nerve. In any of these
approaches, however, the proposed system also utilizes what the
patentees regard as the natural distortion-free transmission of
sound through the ossicular chain wherever possible. They say that,
by virtue of leaving the ossicular chain intact, the acoustic
energy impinging upon the eardrum passes through the ossicular
chain in a distortion-free manner whereby the sound powered hearing
aid they describe needs only supply minimal assistance to the
hearing process. The description continues in the '748 patent to
note that, as an alternative, the stapes may be removed and the
hearing aid physically located in its stead where conditions
permit. Under those circumstances, where the stapes is removed, the
end of the incus is free-standing and the hearing aid is physically
associated with it, such as by means of claimable rings or the
like. Thus the hearing aid serves as an integral part of the
mechanical linkage in the transmission of forces from the eardrum
to the oval window in all events, whether or not the integrity or
continuity of the ossicular chain remains unimpaired. That being
the case, mechanical feedback through the ossicular chain is a
likely consequence, diminishing the overall efficacy of the
approach suggested there.
Another example of an implantable hearing aid is described in U.S.
Pat. No. 3,882,285 issued to J. A. Nunley et al. on May 6, 1975 and
commonly assigned with the present invention. In accordance with
the Nunley et al. invention, a self-contained miniature hearing
device is implanted in the skull just behind the ear (pinna). The
device includes a transducer, such as a microphone, a microphone
port, an amplifier and a transmitter for providing a mechanical
response to the sound received by the microphone. The microphone
port is positioned in the ear canal. The transmitter of the
preferred exemplary embodiment of Nunley et al. utilizes a
piezoelectric crystal connected to the ossicular chain, preferably
to the stapes.
An alternative hearing aid design, the cochlear implant, has
received a modest amount of attention in the prior art. The
cochlear implant is an electronic device that allows profoundly
deaf people to "hear" by electrical stimulation of the auditory
nerve fibers within the inner ear. A typical system includes an
external microphone, signal processor and transmitter, and an
implanted receiver and electrode. The microphone transponds normal
sound waves, converting this mechanical sound energy into
electrical energy representative thereof. The processor amplifies
the electrical energy, filters it and sends it to the transmitter,
which changes the electrical signals into magnetic signals.
Transcutaneous magnetic currents cross the skin and are received by
the implanted receiver, a coil for example, and the signal travels
to the cochlea via a wire electrode. Current flows between this
active electrode and a nearby ground electrode, preferably disposed
in the eustacian tube, to stimulate nerve fibers present in the
cochlea. The brain interprets this stimulation as sound. See T.
Kriewall, "Why Combine Multichannel Processing With A Single
Electrode", Hearing Instruments, June 1985; W. House, D. Bode, and
K. Berliner, "The Cochlear Implant: Performance of Deaf Patients",
Hearing Instruments, September 1981 (both issues of the above cited
publications focus entirely on cochlear implants and are
incorporated herein and relied upon). See also U.S. Pat. No.
3,764,748, discussed above, for a variation on this theme.
The prior art systems, however, admit of room for improvement in
that these known devices tend to be susceptible to interference by
extraneous sounds and/or distortion of the sound ultimately
perceived by the subject. Other prior art systems utilize
air-induced microphones disposed to be responsive to soundwaves for
generating an electrical signal from which the stimulus to the
inner ear is ultimately derived. Air-induced microphones are
disadvantageous in that the microphone is typically either disposed
external to the skull or requires a percutaneous element such as a
microphone port or connecting wire. Moreover, the frequency
response of air-induced microphones tends not to provide sufficient
frequency range for realistic fidelity, and such microphones
typically do not provide constant frequency sensitivity across
their frequency band.
In the aforementioned presentation, "Conservative Tympanoplasty" by
Jako et al., it was proposed that a relatively large piezoelectric
crystal pickup transducer be built into the place of the tympanic
membrane and directly drive a smaller piezoelectric crystal output
transducer placed in the oval window. See Jako et al., supra, at
pages 53-54. However, the Jako et al. system has reportedly never
been reduced to practice, and the practicability of the system was
noted as questionable by the authors themselves (See p. 53).
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for improving
the impaired hearing of a subject utilizing a device manifesting a
frequency response commensurate with that provided by normal
hearing. In accordance with one aspect of the present invention,
the mechanical vibrations effected by the tympanic membrane
(eardrum) are converted into electrical signals which are
thereafter amplified and converted into mechanical vibrations and
communicated to the inner ear. Conversion of mechanical energy to
electrical energy is achieved by means of an input transducer which
is surgically implanted within the ossicular chain, followed by
suitable amplification of those electrical signals to account for
both the level of hearing impairment suffered by the subject and
the electromechanical response of the implanted device. In one
implementation of the present invention, the signals are converted
to mechanical energy (vibrations) once again by an output
transducer, all to achieve the desired level of aural enhancement
for the wearer. These transducers and the associated circuitry thus
comprise means for mediating mechanical/electrical energy within
the middle ear space. In another preferred implementation, the
electrical output of the transducer is suitably conditioned and
applied as a direct electrical stimulus to or proximate the
cochlea. In all instances the ossicular chain of the subject is
interrupted to preclude transmission of mechanical vibrations
between the tympanic membrane and the inner ear, with the implanted
device interposed within the chain to bridge the interruption
therein and form an electromechanically independent link, free from
feedback, between the membrane and the inner ear.
In a particularly preferred variant of the present invention, the
implanted device includes an input transducer means operatively
associated with or proximate the eardrum for receiving mechanical
tympanic vibrations therefrom and converting them into electrical
signals characteristic of the acoustic energy creating those
vibrations. Those signals are applied to appropriate electronic
circuitry to amplify and perhaps otherwise control or condition
them as may be required or found desirable. Those signals are then
communicated to the inner ear, for example by electrode penetration
of the oval window or round window, or by direct electrical
stimulation of the promontory, a bony bulge in the wall of the
tympanic cavity (middle ear space) defined by the region in which
the cochlea protrudes into the cavity. The transducers may be of
any convenient and efficient design, including piezoelectric film
transducers, piezoelectric crystal force transducers, piezoelectric
accelerometers, or electromagnetic transducers. Preferred are the
piezoelectric transducers, and most preferred is a piezoelectric
transducer in an accelerometer configuration.
BRIEF DESCRIPTION OF THE DRAWING
Preferred exemplary embodiments of the present invention will
hereinafter be described in conjunction with the appended drawing
wherein like designations denote like elements and:
FIG. 1 is a schematic section through a portion of the skull of a
human subject adjacent to the ear showing the disposition of one
embodiment of an implantable hearing aid in accordance with the
present invention;
FIGS. 2-5 are schematic illustrations of respective alternative
mechanical connections between the transducers and the hearing
apparatus of the subject;
FIG. 6 is a schematic illustration of a further embodiment of the
present invention utilizing polymeric piezoelectric film
transducers;
FIG. 7 is a schematic illustration, partly in section, of a
preferred alternate embodiment, showing a transducer in an
accelerometer configuration; and
FIG. 8 is a schematic illustration of a further preferred
embodiment of the present invention utilizing an accelerometer,
having wires leading to a power supply, and an electrode, shown
penetrating the cochlea through the footplate of the stapes and the
oval window.
DETAILED DESCRIPTION OF A PREFERRED EXEMPLARY EMBODIMENT
Referring to FIG. 1, a first embodiment 10 of an implantable
hearing device in accordance with the present invention is shown
disposed in a surgically developed antrum 12 in the mastoid bone of
the subject's skull 14, communicating with the subject's middle ear
space 16. Device 10 in this embodiment is comprised of a power
source 18, an amplifier 20, a mechanical to electrical input
transducer 22 and an electrical to mechanical output transducer
24.
Referring briefly to FIG. 2, input transducer 22 and output
transducer 24 suitably each comprise a piezoelectric element 202
cooperating with a resilient diaphragm 204. A connecting member
208, mounted on and maintained by diaphragm 204, is operatively
coupled to piezoelectric element 202. Connecting member 208
advantageously is a 0.005 inch diameter stainless steel wire. (The
respective wires 208 associated with input transducer 22 and output
transducer 24 will be referenced as 208A and 208B, respectively.) A
sleeve 206, mounted to housing 204, and slideable retaining wire
208 may be employed to prevent lateral movement and dampen any
spurious vibrations.
Input transducer 22 cooperates with tympanic membrane 26 and
converts tympanic vibrations corresponding to sound into electrical
signals. Input transducer 22, in effect, utilizes tympanic membrane
26 in a manner similar to the diaphragm of a microphone. With
reference now to FIGS. 1 and 2, the input transducer 22 is
mechanically coupled to tympanic membrane 26, suitably by
connecting stiff wire 208A to the subject's malleus 30. Connecting
wire 208A may be affixed to malleus 30 utilizing surgical
techniques similar to those used in ossicular reconstructive
surgery, or by other desirable techniques or mechanisms. Examples
of connection mechanisms will be described in conjunction with
FIGS. 3-5. When sound waves, generally indicated as 60, impinge
upon tympanic membrane 26, corresponding tympanic vibrations are
initiated. The vibrations are transmitted to malleus 30, and
therefrom, through wire 208A to input transducer 22. The mechanical
vibrations are converted by piezoelectric element 202 (FIG. 2) to
electrical signals. The electrical signals are then applied as
input signals to amplifier 20.
The use of the tympanic membrane as an operative portion of the
input transducer is particularly advantageous. On the one hand,
permanently percutaneous elements, e.g. wires, ports to the ear
canal, etc., typically associated with other input mechanisms such
as air-induced microphones, are avoided, and this can be important
in many situations. In any event, without regard to the avoidance
of percutaneous elements, a principal operational advantage is
realized because the frequency response of the input transducer is
in main part determined by the tympanic membrane and other
characteristics of the individual subject's hearing mechanism and
thus tends to more nearly approximate the frequency response of the
subject's normal aural apparatus.
Amplifier 20 operates on the input transducer electrical output
signals to generate corresponding amplified input signals to output
transducers which are of sufficient magnitude to drive the output
transducer element 202, and which compensate for deficiencies in
the frequency sensitivity of the subject. Amplifier 20 is typically
of the thin film type and suitably comprises any conventional
amplifier circuit having input and output electrical impedances in
accordance with the electrical impedances of transducers. The
frequency response of the amplifier circuit is shaped, as is well
known in the art, to compensate for frequency sensitivity
deficiencies of the subject. The magnitude of the output signals
from amplifier 20 is also limited to a predetermined maximum value
to prevent possible injury (acoustic trauma) to the inner ear. The
power source 18 for amplifier 20 is preferably a long life lithium
type battery.
Output transducer 24 is utilized to convert the amplified
electrical signals representing the tympanic vibrations into
mechanical vibrations for application to the inner ear 28 of the
subject. The amplified electrical signals are applied as input
signals to the piezoelectric element 202 of output transducer 24
and are converted into corresponding mechanical vibrations. The
vibrations are communicated to the inner ear by a mechanical
connection between wire 208B and the oval window 50 or round window
56, and therethrough to the cochlea 51. The connection between wire
208B and the inner ear can be made in a manner similar to
techniques employed in reconstructive surgery using passive
mechanical prosthesis deices or by any other suitable mechanism.
Exemplary connections will be described in connection with FIGS.
3-5.
As noted above, the mechanical connections between input transducer
22 and tympanic membrane 26 and between output transducer 24 and
inner ear 28 are effected utilizing surgical techniques similar to
those used in ossicular reconstructive surgery, or by other desired
methods. The connections are suitably made by affixing the distal
end of stiff wire 208 to an appropriate portion of the ossicular
chain, and a portion of the ossicular chain is then utilized as an
integral part of the mechanical connection.
With respect to input transducer 22, the distal end of wire 208A is
shown to be affixed to the subject's malleus 30, preferably to the
head 34 of malleus 30. For example, as shown in FIG. 3, a small
hole 36 may be drilled in the malleus head 34 and the distal end of
wire 208A received and secured in hole 36. Wire 208A may be secured
by suitable biocompatible cement such as an acrylate ester or
fibrin cement. In some instances, wire 208A may be fixed to malleus
head 34 solely through use of a biocompatible cement without the
necessity of hole 36. Alternatively, as schematically shown in FIG.
4, the coupling to malleus 30 can be effected through use of an
intermediary fitting (cap) 38, articulating with malleus head 34.
It may, however, be desirable in some circumstance to affix wire
208A to portions of the malleus 30 other than head 34. For example,
as shown in the embodiment of FIG. 1, the distal end of wire 208A
may be looped about the neck 32 of malleus 30. Alternatively, wire
208A may be coupled to the tip of the manubrium 42 of malleus 30.
Such a connection is schematically shown in FIG. 5. The attachment
is preferably effected utilizing biocompatible cement as noted
above, or by drilling a hole in manubrium 42 for receiving the
distal end of wire 208A.
With respect to output transducer 24, the distal end of wire 208B
is suitably affixed to the subject's stapes 52. As schematically
shown in FIG. 1, the distal end of wire 208B may be looped about
the capitulum 54 of stapes 52, or, as schematically shown in FIG.
4, an intermediate fitting 56 articulating with capitulum 54 may be
employed. Likewise, the connection can be effected utilizing
biocompatible cement. In some instances, it may be desirable to
effect a connection between 208B and the crus or footplate portions
of the stapes or directly to the oval window in accordance with
well known reconstructive surgical techniques.
It may, however, be desirable in some circumstances, to effect a
connection between wire 208B and the round window 56 rather than to
the oval window. A direct connection to the round window input to
the cochlea may be effected utilizing a device fashioned from
biocompatible materials simulating a footplate disposed over the
round window membrane, to which wire 208B is attached.
In accordance with another embodiment of the present invention, one
or both of input transducer 22 and output transducer 24 can be
formed from a polymeric piezoelectric film such as polyvinylidene
fluoride (PVDF) disposed directly on an appropriate element of the
subject's physical hearing apparatus and electrically connected to
amplifier 20. One such embodiment of the present invention is
illustrated in FIG. 6, wherein respective PVDF film 622 and 624 are
utilized as the input and output transducers, respectively. Input
transducer PVDF film 622 is disposed on the inner surface of
tympanic membrane 26, underlying the manubrium 42 of malleus 30.
Alternatively, PVDF film 622 could be disposed on malleus 30,
preferably on the underside of the manubrium or otherwise
interposed between the tympanic membrane 26 and the underside of
the manubrium of malleus 30. Film 622 is electrically connected to
the input terminals of amplifier 20.
Input transducer PVDF film 624 is disposed on stapes 52, or
directly on oval window 50 or round window 56, and is electrically
connected to the output terminals of amplifier 20. When soundwaves
impinge on tympanic membrane 26 and generate tympanic vibrations,
such vibrations are sensed by film 622 and converted into
electrical signals for application to amplifier 20. The amplified
electrical signals are then applied to output transducer film 624
which converts the amplified signals into mechanical vibrations for
transmission to the inner ear.
The ossicular chain is broken in implementing the present invention
to prevent positive feedback of the amplified vibrations to the
input transducers from occurring. The break would typically be
effected by removing at least one of the component parts of the
ossicular chain, typically the incus. It is desirable to maintain
the malleus and stapes in normal anatonomical position with muscle
and tendon intact to maintain the subject's natural defense
mechanism against acoustic trauma.
FIG. 7 illustrates an alternate embodiment of an implantable
hearing aid 700 in accordance with the present invention. The
hearing aid 700 is comprised of paired transducer means for
mediating electrical/mechanical signals, in this instance a first
or input transducer means designated generally as 702 and a second
or output transducer means designated generally as 704. The
transducers are powered by a power supply 706 disposed within an
antrum formed in the bony structure proximate the ear of the
subject receiving the implant. The input transducer 702 is
operatively associated with the head 34 of the malleus 30 which
vibrates in response to movement of the eardrum as acoustical
energy impinges upon it. The transducer 702 in this embodiment is
shown to be in the configuration of a piezoelectric accelerometer,
comprised of a piezoelectric bimorph 708 having a first
piezoelectric crystal element 710 lying in generally face-to-face
relationship with an opposed crystal 712. The bimorph 708 is
cantilevered at its first end 714 from an enveloping structure or
implanting shield 716, the terminal edges of which are secured to
the head 34 of malleus 30 by means of a suitable biocompatible
adhesive or other surgically acceptable means. The accelerometer
configuration is achieved in this embodiment by a structural weight
718 secured to one of the crystals such as crystal 712 at the end
opposite that cantilevered from the implanting shield 716. In this
configuration, when the malleus vibrates coincident with tympanic
vibrations the weight 718 imparts an inertial response to the
bimorph 708 which will itself then vibrate in a mechanical pattern
replicating the vibration of the malleus. Recognizing that the
forces extant the tympanic membrane have been determined to be
extraordinarily intense, beyond that previously appreciated, the
accelerometer configuration offers enhanced efficiency. Then too,
since the bimorph 708 is cantilevered or otherwise anchored
directly from the mounting structure, the problems inherent in the
placement of these types of elements within a mucuous membrane
environment are greatly alleviated.
Vibrations in the accelerometer are converted to electrical signals
as a consequence of the inherent characteristics of piezoelectric
crystals. These electric signals are applied via signal leads 720
to an amplifier 722. Depending upon the characteristics of the
amplifier 722, a suitable or sufficient gain may be realized
allowing those electric signals to be applied directly to the
output or second transducer 704; otherwise the amplifier 722 may be
used as a preamp and a separate amplifier associated with the
transducer 704 will be provided. Regardless, the signals from
amplifier 722 are routed through the middle ear space via signal
lines 724 for ultimate application to the output transducer. In
this context, the signal leads along with the associated amplifier
circuitry thus constitute transmission means for communicating
between the input and output transducers in lieu of communication
through the ossicular chain.
The output transducer of this embodiment is a bimorph piezoelectric
crystal structure comprised of a pair of piezoelectric crystals 726
and 728 cantilevered at a first end from a support element 730. The
support element 730 is mounted on an arm 732 secured to a bony
region of the subject by means of fixture elements 734, such as
surgical screws. This fixturing approach is conceived to be most
reliable physically and functionally due to the difficulty of
implanting devices in the mucous membrane environment of the middle
ear. The mounting member 732 thus places the output transducer 704
in proximate contact with the stapes 52 whereby vibrations in the
output transducer 704 are communicatively coupled thereto.
Depending upon the electrical characteristics of the amplifier 722
as noted above, an optional amplifier 736 may be provided for
driving the output transducer 704. These matters, however, which
can be tailored at the time the device and its associated circuitry
are designed.
As is evident from the description of the structure in FIG. 7, it
can be seen that the transducers 702 and 704 are surgically
interposed within the ossicular chain in replacement, in this
instance, of the incus. The transducers and associated circuitry
bridge the interruption in the ossicular chain resultant from
removal of the incus to form an independent link between the
tympanic membrane and the inner ear. In this fashion the potential
for mechanical feedback is entirely eliminated, resulting in both
improved efficiencies and comfort to the subject. And, when it is
the incus which is removed in order to interrupt the ossicular
chain and prevent transmission of mechanical vibrations, the
skeletomuscular network of the subject maintains the natural
defense mechanism against acoustic trauma should excessively loud
noises be encountered.
FIG. 8 illustrates an alternate and highly preferred embodiment of
an implantable hearing aid 800 in accordance with the present
invention in which a modified hearing response is effected by
direct electrical stimulation of the inner ear. Hearing aid 800 is
comprised of a single transducer means 818 secured to malleus 30 by
conventional surgical procedures. Transducer 818 is powered by a
power supply 706, preferably disposed within an antrum formed in
the bony structure proximate the subject's ear. Power supply 706 is
shown connected to transducer 818 by electrical connection 806. If
power supply 706 cannot the conveniently disposed intracranially,
percutaneous electromagnetic transmission of the electrical signal
to an external power source may be employed.
Transducer 818 is operatively associated with the head 34 of
malleus 30 which vibrates in response to movement of the eardrum as
sound waves impinge thereon. Transducer 818 is preferably comprised
of a piezoelectric accelerometer in accordance with the
above-described bimorph configuration (see description of the
embodiment of FIG. 7). In contrast to the above-described
embodiments, however, the electrical signals produced by transducer
818 are not converted back into mechanical signals; rather, the
electrical signals themselves stimulate cochlea 51 directly to
effect a modified hearing response. Notwithstanding the fact that
the coupled transducer configuration disclosed above is truncated
in this embodiment, for direct electrical stimulus of the auditory
nerve, the hiatus created in the ossicular chain once again
precludes feedback or competing paths between the tympanic membrane
and the cochlea.
Hearing aid 800 further comprises transmission means 802, which may
be a wire electrode, having a proximal end 812 disposed in
operative communication with transducer 818, and a distal end 816
disposed in electrical communication with inner ear 28. Inner ear
28, or the labyrinth, is comprised of an upper portion 814 (the
vestibule), which controls equilibrium and balance, and a lower
portion 51 (the cochlea), which is the auditory portion related to
hearing. Auditory nerve fibers are located along the inner walls of
cochlea 51, and are collectively referred to as the organ of Corti.
Electrical stimulation of the auditory nerve fibers is achieved via
invasion of cochlea 51 by transmission means 802.
In one preferred method, stapes 22 is removed and distal end 816 of
transmission means 802 is disposed in cochlea 51 by penetrating the
oval window membrane located on promontory 810 beneath foot plate
804 of stapes 22. Alternatively, stapes 22 remains in place and a
hole is drilled in foot plate 804 of stapes 22, using conventional
surgical techniques. Distal end 816 of transmission means 802 is
then guided through the hole, through oval window membrane, and
into cochlea 51, as shown in FIG. 8. In yet another alternate
embodiment, stapes 22 is left intact, and distal end 816 of
transmission means 802 invades cochlea 51 through round window
56.
If penetration of the cochlea is undesirable, electrical
stimulation of cochlea 51 may nonetheless be effected; distal end
816 of transmission means 802 may be secured to the middle ear
cavity membrane along promontory 810 by conventional surgical
techniques.
It will be understood that the above description is of preferred
exemplary embodiments of the present invention and that the
invention is not limited to the specific forms shown. For example,
it is not necessary that each of the components in the embodiment
of FIG. 1 be disposed in a unitary housing. Rather, the various
components can be physically separated. Further, the respective
components may in some instances be disposed in the natural middle
ear space of the subject, rather than in a surgically developed
antrum. These and other modifications may be made in the design and
arrangement of the components without departing from the spirit of
the invention as expressed in the appended claims.
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